U.S. Pat. No. 4,478,083 relates to an ultrasonic tomography unit with an ultrasonic sending/receiving system designed for line-by-line scanning from a number of angular directions of an object under study. The ultrasonic sending/receiving system includes ultrasonic heads, individually or in groups, which scan the object under study line-by-line from various angular directions and which can be focused in corona or corona-like scanning levels at various object depths, and to which are assigned an adjustment device for adjusting the tilt angle of the respective sending/receiving beam, as well as a time gate circuit to permit signal data from the various object depths in the focus ranges to be received in sections.
The groups of ultrasonic heads can be designed in different ways. For example, the ultrasonic heads can include transducer elements, which, for example, can be set up as a linear array, an array for electronically controlled sector scanning, or as a ring array. However, the ultrasonic head can also include an individual ultrasonic transducer, which might be a component of a slowly rotating sector scanner. In addition, the ultrasonic heads can also be arranged at intervals on the circumference of a rotating disk. The disk rotates (together with the mechanical sector scanners) around the axis passing through the object to be investigated. To generate the sector scanning fields, the sector scanners may have a simple swivel motion. In addition, the individual sector scanners may also be scanners that rotate through a full circle. In both cases the frequency of rotation of the disk is much lower than the frequency with which the sector scanner is swiveled or rotated. Thus, for example, the rotational speed of the annular disk together with the sector scanner might be about 0.1 Hz. The swiveling or rotational frequency of the sector scanner, on the other hand, is about 3 or 4 Hz. An ultrasonic array may also be used as an ultrasonic head. This ultrasonic array can, for example be a linear array or an array with an electronically controlled beam sweep for sector scanning, which is likewise rotated slowly along an arc about the axis passing through the object to be investigated. The linear array is preferably a multi-line array in which the individual transducer elements are arranged in a matrix. A variety of apertures can be obtained for sending and/or receiving, using the conventional practice of electronic connection or disconnection of individual elements, thereby forming beam groups of various sizes. In addition to a linear array, which scans the object under study in a linear manner, a ring array is also provided, in which case the beam sweep and its step-by-step progression along the ring array takes place by purely electronic means.
One purpose of the invention, then, is to improve an ultrasonic tomography unit of the kind described above. Another object is to scan several parallel section planes one after the other or even approximately simultaneously, without additional mechanical movement.
In accordance with the invention, the ultrasonic head is a linear array, which consists of a plurality (preferably several hundred) linearly arranged transducer elements. This array is perpendicular to a section plane of the object under study, and can also be rotated about its longitudinal axis. Several groups, each consisting of jointly controlled transducer elements, form in each case a beam aperture. These beam apertures, each of which consists of a plurality (advantageously at least 15 and preferably 30) of linearly arranged transducer elements, are simultaneously stepped by electronic means, for example, according to a group stepping system, advantageously according to a half-step process and preferrably according to a modified half-step process. Between every two adjacent driven groups there is provided at least one group that is switched off. By designing the ultrasonic tomography unit in this manner, it is possible to scan several parallel section planes at least approximately simultaneously.